In these years, adverse influence of the gas, which is generated upon combustion of petroleum fuel, on terrestrial environments creates problems, and as a means for acquiring energy such as power and heat with no generation of waste gases including carbon dioxide and nitrogen dioxide, fuel cells are developed in consideration of environmental preservation.
Of fuel cells, solid electrolytic a fuel cell composed of a separator, fuel electrode, solid electrolyte, gas-diffusion electrode and a separator has compact size and light weight, and its utilization in various fields is under investigation.
Separators in solid electrolytic fuel cells are formed of electrically conductive material to allow taking out of electric power, which are normally provided with uneven grooves on their surfaces for efficient permeation of the reactive gases (oxygen, hydrogen or the like) which are generated at the electrode surface. As the material for separators having such function and configuration, graphite has been conventionally used. Graphite, however, is expensive and requires high skill for its cutting processing, and also is subject to a problem in physical strength.
It was proposed, therefore, to use as the separators flat sheet-formed conductive metallic materials with or without uneven grooves formed on their surfaces, which are coated with electrically conductive paint. (Those separators with unevenly formed surfaces are called ribbed separators.) Generally speaking, it is difficult to uniformly apply electrically conductive paint on metallic material surface by such means as spray coating or roller coating. In particular, with ribbed separators it is extremely difficult to uniformly form an electrically conductive coating film thereon.
JP 2004-31166A discloses electrocoating metallic separators of solid electrolytic fuel cells with electrodeposition paint containing electrically conductive powder such as metal powder, metal-coated powder, carbonaceous powder or the like. However, so obtained coating film fails to reach the levels of conductivity, intimate adherability, corrosion resistance and acid resistance required by users (for example, as to electric resistance, the coating film is required to have a value not higher than 50 Ω) and, furthermore, shows degraded finish, e.g., occurrence of pinholes.